World War I started on this day in 1914 -- this GIF shows how that massive conflict swept the globe

Imperial War MuseumEight-inch howitzers of the 39th Siege Battery, Royal Garrison Artillery firing in the Fricourt-Mametz Valley during the Battle of the Somme, 1916.

World War I started on July 28, 1914, just a month after Austro-Hungarian Archduke Franz Ferdinand and his wife were gunned down on the streets of Sarajevo, Bosnia, by a Serbian nationalist.

The assassination, and the subsequent political and military upheavals, led to the outbreak of war, which would eventually roil much of the globe.

Three bloody years later, the US would be drawn into the conflict on the side of the Allies, declaring war on the Central Powers on April 6, 1917.

Though the war was sparked by regional tensions, a web of entangling defensive alliances quickly pulled in almost the entire world and hastened the end of the European empires.

In May 2014, Reddit user Srirachachacha shared this map showing how the conflict spread across the world, distinguishing between Allied and Central Powers and their colonies, dominions, and territories.